What is the difference between useEffect() and useLayoutEffect()?

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useEffect()

• Runs asynchronously after the browser paints the screen.

• It’s non-blocking, meaning React updates the UI first and then executes the effect.

• Best for tasks like fetching data, setting up subscriptions, or logging, where visual flicker isn’t an issue.

• Example use: updating the document title, calling an API, event listeners.

useLayoutEffect()

• Runs synchronously after all DOM mutations but before the browser repaints.

• It blocks the painting process until the effect finishes, ensuring the DOM is updated before the user sees it.

• Best for tasks that require measuring DOM elements, synchronizing layout, or making visual adjustments.

• Example use: reading element sizes, scroll positions, or applying animations immediately.

Key Difference in a Line

• useEffect() → Runs after paint, doesn’t block UI → used for non-visual side effects.

• useLayoutEffect() → Runs before paint, blocks UI until done → used for DOM measurement and layout adjustments.

Read More :

What are hooks in React? Name some commonly used hooks.

Explain the difference between state and props in React.

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